In the normal process of making a commercial beer, barley malt is mixed with water to form a mash. The enzymes present in the malt are then allowed to break down the barley protein. Next, adjuncts such as cooked corn or rice, are added to the mash to provide additional starch. The enzymatic conversion of the starch to sugar is then permitted to take place. After the starch conversion is more or less complete, the aqueous extract or wort is separated by filtration from the spent solids, which are commonly known as "brewer's spent grain." The hops are added during the boiling of the wort. The hops are removed and the hot wort cooled and aerated. The cooled wort is then inoculated with yeast and allowed to ferment to completion. When the yeast has settled, the immature beer is pumped into refrigerated storage tanks where it is allowed to age. When the aging is complete, the beer is clarified, carbonated under pressure, packaged and pasteurized.
The brewer's spent grain contains all the solids which are separated from the wort by filtration; it includes what is left of the barley malt and the adjuncts. Substantial quantities of brewer's spent grain are produced in the commercial production of beer. Normally, for each barrel of beer at least 8 to 12 pounds of spent grain solids are produced. The breweries usually dispose of the spent grain by selling it for cattle feed.
The brewer's spent grain, which resembles ground grain normally contains, on a bone dry basis, from 28% to 30% protein and from 50% to 55% dietary fiber. It is a good, inexpensive cattle feed. However, as cattle feed, it must compete with other even less expensive agricultural by-products, surplus grain and grazing.